Ab initio density functional theory study of non-polar (101¯), (112¯) and semipolar {202¯1} GaN surfaces

Abstract

The atomic structures of non-polar GaN(101¯0), (112¯0) and semipolar GaN(202¯1), (202¯1¯) surfaces were studied using ab initio calculations within density functional theory. The bulk-like truncated (1 × 1) structure with buckled Ga-N or Ga-Ga dimers was found stable on the non-polar GaN(101¯0) surface in agreement with previous works. Ga-N heterodimers were found energetically stable on the GaN(112¯0)-(1 × 1) surface. The formation of vacancies and substitution site defects was found unfavorable for non-polar GaN surfaces. Semipolar GaN{202¯1}-(1 × 1) surface unit cells consist of non-polar {101¯0} and semipolar {101¯1} nano-facets. The {101¯1} nano-facets consist of two-fold coordinated atoms, which form N-N dimers within a (2 × 1) surface unit cell on a GaN(202¯1) surface. Dimers are not formed on the GaN(202¯1¯) surface. The stability of the surfaces with single {101¯0} or {101¯1} nano-facets was analyzed. A single non-polar {101¯0}-(1 × 1) nano-facet was found stable on the GaN(202¯1) surface, but unstable on the GaN(202¯1¯) surface. A single {101¯1} nano-facet was found unstable. Semipolar GaN surfaces with (202¯1) and (202¯1¯) polarity can be stabilized with a Ga overlayer at Ga-rich experimental conditions.